Ceramic-to-metal seal



3,3fifiA09 Patented Jan. 30, 1908 Hire CERAMIC-TQ-METAL SEAL lfred Milch, Teaneck, N.Ii., and Joseph .i. Lalak, Briarcliff Manor, and Richard H. Airiert, Spring Valley, N.Y., assignors to North American Philips Company, line. No Drawing. Filed June 10, 1965, Ser. No. 463,041

7 Claims. (Cl. 287-189.!065) ABSTRACT OF THE DISCLOSURE A hermetic ceramic-to-metal seal employing a spongy refractory metal layer adjoining the ceramic covered and filled with an alumina-containing material which hermetically seals the spongy metal layer.

Our invention relates to 'ceramic-to-metal seals and to a method of joining ceramics to metals in a vacuum tight manner. In particular, the invention relates to a method of joining a refractory metal such a molybdenum or tungsten to an alumina ceramic.

In a copending application, Serial No. 269,133, filed Mar. 29, 1963, a method of joining bodies, one of which may be metal and the other ceramic is disclosed. In that method, the surfaces of the bodies to be joined are covered with a bonding material which contains CaO or BaO, A1 and MgO or $10. The bonding material then is heated to a temperature exceeding 1300 C. to form a melt whereafter the bonding material is cooled to solidify it.

We have found that seals made in this manner are relatively weak. There is no evidence of chemical attack of the bonding material on the metal, 1:6. the bond appears to depend solely upon physical contact between the metal surface and the fused bonding material.

A principal object of our invention is to improve the mechanical strength of the seal described above without impairing its impermeability or high temperature resistance.

A further object of our invention is to provide a ceramic'to-metal seal which is resistant to attack by cesium vapor.

Another object of our invention is to provide an improved method of joining a refractory metal to an alumina ceramic.

Further objects of the invention will appear as the specification progresses.

In accordance with the invention, a strong but porous bond is formed between the metal and ceramic member to be joined and then the joint is rendered vacuum-tight by means of the bonding materials disclosed in application Ser. No. 269,133.

Thus, in a particular embodiment of the invention which is exemplary thereof, a suspension of molybdenum oxide in amylacetate nitrocellulose solution first was applied between the metal and ceramic members to be joined and the assembly fired in wet hydrogen at 1650 C. brightness or higher for approximately minutes under slight pressure. This resulted in a porous but quite strong bond of molybdenum between the metal and ceramic. This joint was then covered with a water suspension of finely-divided A1 0 and CaCO in a mol ratio of SCaO The assembly was reheated to 1650" C. brightness for twenty minutes to decompose the carbonate and to allow the mass to fuse over and into the molybdenum joint.

Alternatively, the molybdenum oxide suspension applied between the ceramic and metal members may be allowed to dry, after which the 5CaCO ::3Al O suspension is applied as an overlayer. The entire firing may then be accomplished in a single step to produce the desired refractory hermetic bond of improved mechanical strength.

A disc of .002" thick molybdenum sheet was thus joined to a one-half inch diameter alumina tube with a 0.050 in wall. The bond that was formed was vacuum tight and resisted attempts to separate the original members to the extent that the molybdenum disc ruptured as the seal was destroyed. Examination of the ruptured molybdenum disc gave distinct evidence of chemical attack by the MoO thus accounting for the increased me chanical strength.

It will be obvious to those skilled in the art that other metals such as tungsten or rhenium may be bonded to other ceramics which can be metallized by tungsten or molybdenum or mixtures thereof, such as spinel, magnesia, sapphire, and the like using the method herein described. Likewise, tungsten oxide may be used as a substitute for or mixed with the molybdenum oxide to form the spongy metal layer on the ceramic. Furthermore, the particular bonding material is exemplary only since any of the those disclosed in application Ser. No. 269,133 may be employed herein. However, it should be noted that because of the extreme chemical reactivity between silica and alkali-metal the bonding material must be free of silica in order to maintain alkali vapor resistance.

Therefore, we do not wish to be limited to the particular materials disclosed herein since the invention is pointed out in the appended claims.

What we claim is:

1. As an article of manufacture, a ceramic body selected from the group consisting of alumina, spinel, magnesia, and synthetic sapphire hermetically bonded to a metal body selected from the group consisting of molybdenum, tungsten and rhenium with a spongy layer of a metal selected from the group consisting of molybdenum and tungsten and mixtures thereof, said layer being filled and covered with a fused mass of an alumina containing material which hermetically seals the spongy metal layer.

2. As an article of manufacture, a ceramic body selected from the group consisting of alumina, spinel, magnesia and synthetic sapphire hermetically bonded to a metal body selected from the group consisting of molyb denum, tungsten and rhenium with a spongy layer of molybdenum, said layer being filled and covered with a fused mass of an alumina containing silica-free material which hermetically seals the spongy metal layer.

3. As an article of manufacture, an alumina ceramic body hermetically bonded to a refractory metal body selected from the group consisting of molybdenum, tungsten and rhenium with a spongy layer of molybdenum, said layer being filled and covered with a fused mass of Cat) and A1 0 in a mol ratio of 5:3 which hermetically seals the spongy metal layer.

4. An an article of manufacture, an alumina ceramic body hermetically bonded to a refractory metal body selected from the group consisting of molybdenum, tungsten and rhenium with a spongy layer of molydenum, said layer being filled and covered with a fused mass of A1 0 and C210 which hermetically seals the spongy metal layer.

5. As an article of manufacture, a ceramic body selected from the group consisting of alumina, spinel, magnesia and synthetic sapphire hermetically bonded to a metal body selected from the group consisting of molybdenum, tungsten and rhenium with a spongy layer of a metal selected from the group consisting of molybdenum and tungsten and mixtures thereof, said layer being filled 3 4 and covered with a fused mass of material composed of References Cited an oxide selected from the group consisting of C210 and BaO, A1 0 and an oxide selected from the group con- UNITED STATES PATENTS sisting of MgO and SrO which hermetically seals the 2,282,106 5/1942 Underwood spongy metal layer, 5 9, 1/1944 Garner 29--l95 6. An article of manufacture as claimed in claim 5 219961401 3/1961 WtFICh 9 9 in which the fused layer of material contains SiO 3,023,492 3/ 1962 BrlStOW 9 95 7. An article of manufacture as claimed in claim 5 in 3,275,358 9/ 1966 shonebafgef which the spongy layer of metal is molybdenum and the ceramic body is 1 0 HYLAND BIZOT, Primary Examiner. 

